A substantial proportion of the prescription drugs dispensed today are in the form of pills, tablets or capsules. They are usually packaged by the pharmacist in an injection molded vial made of a thermoplastic material. The vial is usually closed with a plastic closure of the snap cap type or a one-piece child resistant closure with or without a liner. The child resistant closures require the simultaneous motions of pushing down and turning. Neither of these closure types makes a tight seal between the closure and the vial.
The National Formulary XIV and the United States Pharmacopoeia XIX have issued current standards for containers for drugs which require packaging and storing in a tight container or a well closed container. The standard includes a Moisture Vapor Penetration test for the container itself and for the closure. The procedure to be employed in the test is described in detail in the National Formulary XIV, pages 888-889. Each container and its closure must be closed tightly and opened 30 times before the test is begun. Then each container is filled with desiccated calcium chloride and sealed with an application torque as stated in the Table below:
______________________________________ Suggested application Container Diameter torque (in inch-pounds) ______________________________________ 28 mm. 11-17 33 mm. 13-20 38 mm. 15-23 43 mm. 17-26 48 mm. 19-29 58 mm. 23-35 ______________________________________
After weighing each individual container, the containers are put in an atmosphere which is controlled as to temperature and humidity for a period of two weeks. They are then individually reweighed to determine the amount of moisture absorbed by the calcium chloride. This is related to the volume of the container to determine the weight of water absorbed stated in milligrams per liter of capacity per day. The weight of the absorbed water should not exceed 100 milligrams of water per liter of capacity per day if the seal is to be classified as tight by industry standards.
The moisture vapor penetration characteristic of a container is important because many drugs are subject to deterioration on prolonged exposure to moisture and many persons keep prescription drugs in the bathroom where the humidity is frequently high. The seal tightness suggested in the test is the standard generally accepted in the closure and container industries, based on their experiences of the torques required to seat a closure on a container sufficiently tight to insure protection of the contents in packages using the normal commercial liners. These liners are mostly wood pulp with a facing of polyvinylidine chloride or Saran. These suggested application torques are much higher than the torques that many of the people using prescription drugs can exert in securing a container cap.
The users of prescription drugs close the container many more times than does the pharmacist. The effectiveness of the seal when the user closes the container is the basic factor in determining whether the purity and efficacy of the drug will be maintained by the package. Many of the users of prescription drugs ar infirm, arthritic or sick. Others think of a closure as merely a device to keep the contents from spilling in the event the container is upset. Random tests in the 28 mm. size closure show that about half of the people normally reclose containers with three inch-pounds of torque and that few persons exert a torque greater than seven inch-pounds on this size closure.